1. Field of the Invention
The present invention relates to a resist composition, a method of forming a resist pattern that uses the resist composition, a novel compound that is useful as an acid generator within the resist composition, and an acid generator.
Priority is claimed on Japanese Patent Application No. 2008-187717, filed Jul. 18, 2008, and Japanese Patent Application No. 2008-298679, filed Nov. 21, 2008, the contents of which are incorporated herein by reference.
2. Description of Related Art
In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive composition, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative composition.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beam, EUV (extreme ultraviolet radiation), and X rays.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material which satisfies these conditions, a chemically amplified resist composition is used, which includes a base component that exhibits changed solubility in an alkali developing solution under the action of acid and an acid generator that generates acid upon exposure.
For example, a chemically amplified positive resist composition typically contains a resin component (a base resin) that exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator component. When a resist film formed from such a resist composition is subjected to selective exposure during formation of a resist pattern, acid is generated from the acid generator by the exposure within the exposed portions, and the action of that acid causes an increase in the solubility of the resin component within an alkali developing solution, causing the exposed portions to become soluble in the alkali developing solution.
Resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1).
In this description, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.
In terms of the acid generator used in a chemically amplified resist, a multitude of different acid generators have been proposed including, for example, onium salt-based acid generators such as iodonium salts and sulfonium salts, oxime sulfonate-based acid generators, diazomethane-based acid generators, nitrobenzylsulfonate-based acid generators, iminosulfonate-based acid generators, and disulfone-based acid generators.
Currently, onium salt-based acid generators containing an onium ion such as a triphenylsulfonium ion as the cation moiety are widely used as the acid generator. The anion moiety of these onium salt-based acid generators is typically an alkylsulfonate ion or a fluorinated alkylsulfonate ion in which some or all of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms (for example, see Patent Document 2).
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-241385
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2005-37888